13 Deviations from the World

What is the set of points whose distance from the same plane to the fixed point is equal to the fixed length? Yes, it is a circle. If the center of the circle does not move, one diameter of the circle is extended or shortened, and its value is greater than or less than any diameter of other circles the same, what will happen? An ellipse based on a circle appears. What if this diameter continues to extend or shorten indefinitely?

Is it possible that the circle will eventually become an infinitely extended straight line? That is to say, the center of the circle will disappear in the end. ......